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"Dust discs" could aid planet-hunters

18 February 2002

By Will Knight

The ring of fine dust that surrounds our solar system is generated from within, according to new data from the European Space Agency’s Ulysses probe. Similar dust rings are likely to circle other star systems containing planets – providing a relatively simple target for astronomers searching for other planets.

Data from Ulysses shows that interstellar dust particles, which enter our solar system from outside, are much finer than those found within a disc of dust that was first detected by NASA’s Pioneer 10 and 11 probes in the 1970s. This disc of dust stretches from Saturn to beyond Pluto.

The ESA researchers say that collisions within a band of debris beyond Pluto known as the Edgeworth-Kuiper Belt must generate the disc of dust. These bodies are remnants of the formation of our solar system.

“In order to sustain such a ring, 50 tonnes of dust have to be generated every second,” says lead researcher Markus Landgraf, at ESA’s Space Operations Centre in Darmstadt, Germany. Landgraf says that detecting dust rings around other stars will provide strong evidence that planets also orbit them.

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Easy targets

Neil McBride of the Open University agrees there is every reason to suspect that other planetary systems will have similar discs of dust. He adds that a large dust disc will be easier to detect than even sizeable orbiting objects, because the dust will have a greater surface area collectively and will radiate more heat.

“They will have a lot more radiating power, and you would see this more readily,” McBride told New Scientist.

Theories that the dust could have been generated by the solar system’s asteroid belt, which lies between Mars and Jupiter, or by passing comets have been ruled out. Beyond Saturn, comets are too cold to spew dust as they move, and dust from the asteroid belt does not travel towards the edge of the Solar System.

“If you have a dust disc around a star that’s not particularly young, then it’s extremely interesting because the dust has to come from somewhere,” says Malcolm Fridlund, of ESA’s Darwin project, which will use an array of probes to search for Earth-like planets after 2014. “The only explanation is that the star has planets, comets, asteroids or other bodies that collide and generate the dust.”

Researchers from the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, Lockheed Martin Space Operations in the US and NASA’s Johnson Space Centre contributed to the research. The findings will be published in The Astrophysical Journal.